1. Field of Endeavor
The present invention relates to microvalves and more particularly to microvalves for use with microcatheters.
2. State of Technology
Microcatheters are used in many medical applications for minimally invasive surgery. It is estimated there are presently over 700,000 surgical uses of catheters per year in the United States representing a market of over $350 million. They can in inserted into arteries or veins and snaked around within the body until their tip is in a desired location. Catheter type devices are also used with minimally invasive techniques including biomonitoring, biosensing and nuclear stockpile monitoring.
U.S. Pat. No. 5,819,749 for a microvalve by Abraham Lee, et al, patented Oct. 13, 1998 provides the following description: xe2x80x9cPresent catheter technology, while significantly improving the outcome of severe trauma and congenital diseases is lacking in technological sophistication. Specifically, catheters lack sub-millimeter-sized distal actuators and sensors, adequate embolic and stenting materials and devices, feedback control (both force and tactile), computer-based autonomous control of steering and actuation, and sufficient imaging/therapy coupling. Presently, the catheter-based procedures for cardiological, neurological, and peripheral vessel repairs and treatments require direct, hands-on, continuous manipulation by experienced physicians. Procedures, especially in the neurological field, can be very lengthy (4-6 hours) and extremely tedious. Some improvements have been made in catheter technology for access; i.e., getting to the site of therapy. Examples are new guidewire materials and reduced sizes of the catheters. As well, there have been new innovations in therapies, especially in the cardiology field. These include balloon angioplasty, laser ablation, stenting, and rotobladers. Most of these are specifically designed to treat arteriosclerosis, and have been minimally successful (restenosis rates of over 35% are common). Most intravascular therapies that are potentially deliverable by catheter methodology are severely limited by the lack of sophistication of the tools themselves, the control of the tools, and the associated technologies such as imaging. By improving and miniaturizing the distal end tools (microtools), providing force and tactile feedback, integrating sensors and autonomous steering, and improving imaging (optical and ultrasound); this very powerful medical technology will be made more usable, widespread, and efficient.xe2x80x9d
U.S. Pat. No. 5,325,880 for a shape memory alloy film actuated microvalve by David Johnson, patented Jul. 5, 1994, provides the following description in its abstract: xe2x80x9cA sub-miniature valve which provides an actuator of shape memory alloy film coupled so as to move a poppet adjacent to a valve port. The shape memory alloy film actuator is thermally cycled through its phase change transition temperature, resulting in either a contraction or elongation of the actuator. This causes the poppet to move relative to the port and either increase or decrease fluid flow. The shape memory alloy film is biased toward its deformed position when cooled below its transition temperature. The valve can be electrically operated with commonly available voltages, including those used for micro-electronics. The relatively large forces and displacements achieved using the shape memory alloy film provide less restriction and greater flow than in other similarly sized valves.xe2x80x9d
World Intellectual Property Organization Patent No. WO9938551 for an implantable drug infusion device having a safety valve, published Aug. 5, 1999, by Koen Weijand, et al, provides the following description: An implantable drug infusion device which features a safety valve. The safety valve is normally in the closed state and only opens upon electrical activation. The valve is designed so as to be constructed in an extremely small size and further to be made of corrosion resistant materials. The valve may be used in either a passive or an active drug infusion system. Also disclosed is an efficient circuit to drive, i.e. open and close, the safety valve. Further disclosed is a timing scheme for opening and closing the safety valve for use in an active drug infusion device.
U.S. Pat. No. 5,634,913 for a softening conduit for carrying fluids into and out of the human body by Florence Stinger, patented Jun. 3, 1997 provides the following description: xe2x80x9cIn the field of catheters, it has been proposed to utilize a polymer material which softens at body temperature and/or upon exposure to moisture. Such catheters are disclosed, for example, in U.S. Pat. Nos. 4,846,812 and 5,441,489, and comprise a rigid portion for manipulation of the catheter and a portion which becomes flexible after insertion into the body. This flexibility can be delayed for a period of time to enable the catheter to be properly positioned. However, when puncturing of the skin is necessary, it is still necessary to make an incision or to puncture the skin with a separate lancet. For example, U.S. Pat. Nos. 4,883,699 and 4,911,691 disclose a catheter formed of a polymer which softens upon absorbing water used in combination with a metal lancet which passes therethrough for puncturing the skin. U.S. Pat. No. 4,955,863 similarly discloses a catheter assembly including a cannula, a needle and a catheter inserter in slidable relationship to the cannula. These devices present the disadvantage that metal lancets are necessary, presenting the safety and disposal problems discussed above. Further, the lancet or guidewire used in connection with the catheter is necessarily longer than the catheter itself, and enters the body first, at which time the practitioner must push the lancet or guidewire further in order to correctly position the catheter. This procedure is a risk to the patient, as the lancet or guidewire may puncture a vessel, membrane, tendon, bone, nerve, lung or spinal cord. Early detection of the appropriate placement of the catheter is not possible with these devices combining a metal lancet or guidewire with a catheter.xe2x80x9d
U.S. Pat. No. 6,102,917 for a shape memory polymer (SMP) gripper with a release sensing system, by Maitland et al, patented Aug. 15, 2000, and assigned to provides the following description: xe2x80x9cA system for releasing a target material, such as an embolic coil from an SMP located at the end of a catheter utilizing an optical arrangement for releasing the material. The system includes a laser, laser driver, display panel, photodetector, fiber optics coupler, fiber optics and connectors, a catheter, and an SMP-based gripper, and includes a release sensing and feedback arrangement. The SMP-based gripper is heated via laser light through an optic fiber causing the gripper to release a target material (e.g., embolic coil for therapeutic treatment of aneurysms). Various embodiments are provided for coupling the laser light into the SMP, which includes specific positioning of the coils, removal of the fiber cladding adjacent the coil, a metal coating on the SMP, doping the SMP with a gradient absorbing dye, tapering the fiber optic end, coating the SMP with low refractive index material, and locating an insert between the fiber optic and the coil.xe2x80x9d U.S. Pat. No. 6,102,917 is incorporated herein in its entirety by reference.
The present invention provides a valve system for catheters and catheter type devices used with minimally invasive techniques such as biomonitoring, biosensing, nuclear stockpile monitoring, chemical delivery systems, and surgical procedures. In one embodiment of the present invention, a bistable microvalve system is provided for use with microcatheters. A bistable microvalve of shape memory material is operatively connected to a microcatheter. The bistable microvalve includes a tip that can be closed off until it is in the desired position. Once it is in position it can opened and closed. The system uses heat to activate the shape memory material. The shape memory material""s elastic modulus will change when heated above a transition temperature. The shape memory material is adapted to move from a first shape to a second shape, either open or closed, where it can perform a desired function. Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description and by practice of the invention.